I am a little concerned about the "sandwich" you made for your top. Plywood and MDF are both products that have virtually no expansion/contraction during changes in relative humidity. However, solid wood like tongue and groove red oak flooring will want to expand and contract during seasonal changes in humidity. This can cause serious problems in keeping the top flat. It will likely warp. Hopefully, it's location will be in an area of minimal moisture change.
That said, here are a couple of suggested treatments for a workbench top.
A film finish (lacquer, shellac, varnish, poly varnish) is not the way to finish a workbench top. A workbench is going to get dinged and film finishes will crack or craze or be otherwise damaged. Once a film finish is penetrated, it looses its effectiveness and adjacent areas begin to fail. No treatment is going to make a soft wood bench-top harder. I much favor a "in the wood finish". Here are two that lots of folks find effective.
First, is an boiled linseed oil and wax finish. Sand the surface to 180 grit. Mix paraffin or bees wax into heated boiled linseed oil. USE A DOUBLE BOILER TO HEAT THE OIL. The ratio is not critical but about 5-6 parts of boiled linseed oil in a double boiler with one part paraffin or beeswax shaved in. Take it off the stove. Thin this mixture about 50/50 with mineral spirits to make a heavy cream like liquid. Apply this mixture to the benchtop liberally and allow to set overnight. Do it again the next day and again the following day if the top continues to absorb it. After a final overnight, lightly scrape off any excess wax and buff. This finish will minimize the absorbsion of any water and you can use a damp rag to wipe up any glue excess. Dried glue will pop right off the surface. Renewal or repair is easy. Just use a scraper to remove and hardened stuff, wipe down with mineral spirits using a 3/0 steel wool pad (a non-woven green or gray abrasive pad is better), wipe off the gunk and apply another coat of mineral oil/wax mixture.
My personal preference is for an oil/varnish mixture treatment. Either use Minwax Tung Oil Finish, Minwax Antique oil or a homebrew of equal parts of boiled linseed oil, your favorite varnish or poly varnish and mineral spirits. Sand the benchtop up to 180 grit. Apply the mixture heavily and keep it wet for 15-30 minutes. Wipe off any excess completely. Let it dry overnight and the next day, apply another coat using a gray non-woven abrasive pad. Let it set and then wipe off any excess. Let this dry 48-72 hours. To prevent glue from sticking apply a coat of furniture paste wax and you're done. This treatment is somewhat more protective than the wax and mineral oil as the varnish component adds some protection from not only water both some other chemicals also. The waxing makes the surface a little more impervious to water so you can wipe up any liquid adhesive. It also allows hardened adhesive to be scraped off. Repair and renewal is easy. Just go throught the same scraping, wiping down with mineral spirits and reapplication of the BLO/varnish/mineral spirits mixture and an application of paste wax.
Both of the above treatments are quite protective but are easy to maintain and renew. They do not fail when the surface takes a ding.